Characteristics, limitations and global regulations in the use of biogas digestate as fertilizer: A comprehensive overview

The utilization of biogas digestate, the effluent of anaerobic digestion (AD), as an organic fertilizer offers promising advances for sustainable agriculture, but it also presents critical challenges that require careful regulatory oversight. This review explores the wide characteristics range of digestate, key limitations, and regulatory frameworks shaping the use of biogas digestate as fertilizer. While digestate is a rich source of essential macro and micronutrients required for promoting plants growth, its application risks leading to nutrient overload, contamination from heavy metals, pathogens, antibiotics, microplastics, and emerging contaminants. By exploring the current regulations managing the utilization of biogas digestate as fertilizer, the EU limits digestate application to 170 kg N/ha/year, with a higher allowance in the UK (up to 250 kg N/ha/year). In other major biogas-producing countries, there is no specific limit for digestate application, as it varies depending on individual cases. Heavy metals and pathogens are satisfactorily regulated in the policies of these countries. However, no specific limits exist for antibiotics and microplastics, despite their significant impact on human health and the environment. Moreover, regulations concerning other potential chemicals are limited. Expanding these regulations is recommended to mitigate associated health and environmental risks.